The invention relates generally to the field of power electronic devices such as those used in power conversion and for applying power to motors and similar loads. More particularly, the invention relates to a motor drive with an improved choke that provides improved protection from the environment.
In the field of power electronic devices, a wide range of circuitry is known and currently available for converting, producing and applying power to loads. Depending upon the application, such circuitry may convert incoming power from one form to another as needed by the load. In a typical arrangement, for example, constant (or varying) frequency alternating current power (such as from a utility grid or generator) is converted to controlled frequency alternating current power to drive motors, and other loads. In this type of application, the frequency of the output power can be regulated to control the speed of the motor or other device. Many other applications exist, however, for power electronic circuits that convert alternating current power to direct current power, or vice versa, or that otherwise manipulate, filter, or modify electric signals for powering a load. Circuits of this type generally include rectifiers (converters), inverters, and power conditioning circuits. For example, a motor drive will typically include a rectifier that converts AC power to DC. Inverter circuitry then converts the DC signal into an AC signal of a particular frequency desired for driving a motor at a particular speed. Often, power conditioning circuits, such as a choke and/or a capacitor bus are used to remove unwanted voltage ripple on the internal DC bus. Depending on the power load, the power conditioning circuits, such as the choke, may conduct high levels of current and generate significant levels of heat.
The housing that holds most of the circuitry described above may be referred to as a cabinet. To dissipate the heat generated by the circuitry inside the cabinet, a motor drive unit will typically include a cooling channel adjacent to the cabinet that conducts cooling air through a heatsink thermally coupled to the circuits. To make efficient use of the space within the motor drive unit and keep heat generated by the choke out of the cabinet and away from other circuit components, the choke is usually deployed within the cooling channel rather than the cabinet. Furthermore, the motor drive may be deployed such that the cooling channel is exposed to the outdoors. Thus the choke may be subject to harsh environmental conditions due to weather, dust, and cleaning.
Therefore, it may be advantageous to provide a motor drive unit with an improved choke that enables increased protection from the environment. In particular, it may be advantageous to provide a choke that enables improved protection from water, dust, and salt.